1. Field of the Invention
The present invention relates to an electronically controlled inductive load actuator, and more particularly an electronically controlled diesel fuel injector.
2. Discussion of Related Art
From the 1960""s to the present there has been increasing awareness of the effect that vehicular emissions have on the environment. Accordingly, increasingly demanding emissions standards have been imposed on vehicles in a number of countries, including the United States.
One way that has been used in the past to control emissions in vehicles is to have an accurate knowledge and control of the start and stop of fuel injection as well as the amount of fuel delivery. One method of such control is to have a rapid rise/fall in current enabling the fuel injection valve to move from a closed to an open position in a very short predictable period of time. This allows for an accurate understanding of the start and stop of fuel injection. Also the faster the armature moves, the more accurate the prediction of fuel flow, especially with the demand for higher fuel rail pressures.
In the past, the rapid rise in current, if the vehicle battery could not provide it, was provided by a boost supply that comprised a capacitor that stored the energy required for the rapid rise in current. The power output of the boost supply and the choice in capacitance involved an understanding of the required current rise rate, load inductance and the minimum spacing between fuel injection events. The rapid fall in current was typically provided by turning off the injection driver abruptly by actively clamping the voltage across the load so as to rapidly dissipate the energy stored in the load. This energy was dissipated as a power loss in the circuit elements.
As shown in FIG. 1, a typical method of driving an inductive load is via a battery B. To drive the load L to a higher current level, both switches S1 and S2 are closed, and current flows from the battery B through S1, the load L, returning to ground via S2. To provide a slow current decay, S1 is then opened causing current to flow through diode D2 and S2. In the alternative, for a rapid decay in current, S1 and S2 are opened so that current flows from ground, through D2, the load L, and returns through diode D1 to the battery B. Note that it is possible to eliminate the diode D1 when the switch S2 operates like an FET or similar type switch so that the current flows from ground, through diode D2, through the load L and returns to ground through the switch S2 when the switch S2 is operating in an unsaturated/linear manner.
In another known structure shown in FIG. 2, the inductive load L is driven by a battery B and an independent boost supply. The output filter is represented by the boost capacitor C. For an initial rapid rise in current, switches S1 and S2 are both closed so that current will flow out of the boost capacitor C and through S1, the load L, returning to the capacitor C via S2. The load L can then be driven to a higher current level via battery B by opening switch S1 and closing switches S2 and S3 so that current flows from the battery B through S3, the load L, and returning to ground via S2. At this point, the current can either decay slowly or quickly. To provide a slow current decay, switch S2 is closed and switches S1 and S3 are opened so that current flows through diode D2 and S2. For a rapid decay in current, switches S1, S2 and S3 are all opened so that current flows from ground, through D2, the load L, and returns to ground through the switch S2 when the switch S2 operates like an FET or similar type switch and the switch S2 is operating in an unsaturated/linear manner.
There has become an increased need for multiple injection events on the same fuel injector during a given engine cycle. These multiple injection requirements add a burden to inductive load driver systems that use a boost supply in that the boost supply is required to provide a given amount of energy to the load repeatedly in rapid succession. For an independent boost supply to provide this energy, the power output requirements and therefore its cost, size, and power losses become excessive.
In an attempt to accommodate these multiple injection events using the known methods described above with respect to the inductive load driver systems of FIGS. 1 and 2, the supply providing the initial current rise may require a substantial power output capability. This is not an issue if the supply is a battery as with the inductive load driver system of FIG. 1. However, for the inductive load driver system of FIG. 2 that uses a separate boost power supply, this could have substantial impact on the design, such as increasing component sizes and costs.
One known way to get around the shortcomings of the inductive load driver system of FIG. 2 is to recovery energy from the load L. Two embodiments and methods for recovering energy from the load L are illustrated in FIGS. 3 and 4. In the embodiment of FIG. 3, when switch S3 is open, switches S1 and S2 are closed to cause current to flow out of the boost capacitor C through S1 so as to cause an initial rapid rise in current in the load L. The current is later returned to the capacitor C through ground via switch S2. To drive the load L to a higher current level through the battery B, switches S2 and S3 are closed while S1 is open. In this case, the current flows from the battery B through S3, the load L and returning to ground through S2. To provide a slow current decay, S2 is closed and S1 and S3 are open so that current flows through D2 and S2. For energy recovery from the load charging the boost capacitor C (which also provides for a rapid decay in current), S1, S2 and S3 are open, current flows from ground, through D2, the load, and returns to the boost capacitor C through D1.
In the embodiment of FIG. 4, an initial rapid rise in current in the load L is caused by closing switches S1 and S2 so that current will flow out of the boost capacitor C through S1, the load L, and returning to the capacitor C via S2. To drive the load to a higher current level through the battery B, switch S2 is closed while switch S1 is open. In this case, current flows from the battery B through diode D2, the load L, returning to ground through S2. To provide a slow current decay, S1 is closed with S2 open causing current to flow through S1 and D1. For energy recovery from the load L charging the boost capacitor C (which also provides for a rapid decay in current), S1 and S2 are open so that current flows from the battery B through D2, the load L, and returns to the boost capacitor C through D1.
Note that the embodiments of FIGS. 3 and 4 are such that the separate boost supply is eliminated and all of the energy required for the initial current rise may be derived from the load(s), since the loads are inductive in nature, and, thus, may be used as the inductive element of a boost supply. Of course, when the load is used for charging the boost capacitor C it is desirable to drive the load with a current that does not actuate the load.
The four methods of operating the prior inductive load driver systems of FIGS. 1-4 are summarized in the table below. In reading the table, the term S2BD denotes the situation when the switch S2 operates like an FET or similar type switch and the switch S2 is operating in an unsaturated/linear manner, i.e., the voltage is clamped to a high voltage during turnoff. The term xe2x80x9cRecirculate/Freewheelxe2x80x9d regards the current slowly decaying from the load due to a slow energy discharge with no energy transfer from the load. The term xe2x80x9cRapid Current Fall/Recoveryxe2x80x9d regards a rapid current decay from the load caused by a rapid energy transfer from the load to an energy storage device like a capacitor C.
Each of the above-described embodiments of FIGS. 1-4 is very similar in that they are each formed with a bridge where the middle element in the bridge is the load inductor. The addition of energy recovery involves maintaining the presence of D1 from the battery drive scheme with the addition of a boost capacitor.
Ignoring how the battery source is connected, the two energy recovery methods described above with respect to FIGS. 3 and 4 have the same topology as shown in FIG. 5. Driving the load from the capacitor C involves closing switches S1 and S2. Slow energy discharge with no energy transfer may be done either through D1, S1 or through D2, S2. Energy recovery or rapid energy transfer from the load to the storage capacitor C involves discharging the inductor into the capacitor through D1 and D2. There are at least two disadvantages to driving the load with this topology. For example, one disadvantage is that multiple current sensing elements are required or an alternate method for the prediction of current fall time while the capacitor is being charged (when current is flowing through D1 and S2 is open) is required since there is no one element that carries the load current at all times. A second disadvantage of the topology is that there is no means for having the load grounded externally, or directly to the engine block so that harnessing requirements increase and assembly is made more difficult so that costs increase.
One aspect of the present invention regards an inductive load driver having an inductive load and a bridge circuit connected in parallel with the inductive load, wherein the bridge circuit generates a current to the inductive load that rises.
The above aspect of the present invention provides the advantage of improving the ease of current sense.
The above aspect of the present invention provides the second advantage of using a single ended load, i.e., only the positive terminal of the load being connected to the driving circuit that allows the load to be grounded externally.
The above aspect of the invention provides another advantage of decreasing both harnessing requirements and the difficulty of assembly.
Further objects, advantages and details of the invention will become apparent from the ensuing description of an exemplary embodiment in conjunction with the accompanying drawings.